[Place of malaria among febrile illnesses in two ethnic tribes living in sympatry in Mali from 1998 to 2008]

Different Plasmodium falciparum clearance times in two Malian villages following artesunate monotherapy

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High prevalence of residual parasitemia at day 3 post-artesunate monotherapy treatment using qPCR while no parasites were detected by microscopy at the same timepoint.

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A longer parasite clearance time observed in a Malian village.

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Artesunate treatment is still efficacious on Plasmodium falciparum in Mali.

Background

Artemisinin resistance described as increased parasite clearance time (PCT) is rare in Africa. More sensitive methods such as qPCR might better characterize the clearance phenotype in sub-Saharan Africa.

Methods

PCT is explored in Mali using light microscopy and qPCR after artesunate for uncomplicated malaria. In two villages, patients were followed for 28 days. Blood smears and spots were collected respectively for microscopy and qPCR. Parasitemia slope half-life was calculated after microscopy. Patient residual parasitemia were measured by qPCR.

Results

Uncorrected adequate clinical and parasitological responses (ACPR) observed in Faladje and Bougoula-Hameau were 78% and 92%, respectively (p = 0.01). This reached 100% for both after molecular correction.

Proportions of 24H microscopy positive patients in Faladje and Bougoula-Hameau were 97.2% and 72%, respectively (p < 0.0001).

Slope half-life was 2.8 h in Faladje vs 2H in Bougoula-Hameau (p < 0.001) and

Proportions of 72H patients with residual parasitemia were 68.5% and 40% in Faladje and Bougoula-Hameau, respectively (p = 0.003). The mean residual parasitemia was 2.9 in Faladje vs. 0.008 in Bougoula-Hameau (p = 0.002).

Although artesunate is efficacious in Mali, the longer parasite clearance time with submicroscopic parasitemia observed may represent early signs of developing P. falciparum resistance to artemisinins.

Ethnic differences in susceptibility to malaria: what have we learned from immuno-epidemiological studies in West Africa?

There are many fundamental aspects of the immunobiology of Plasmodium falciparum infections that are not fully understood, therefore limiting our comprehension of how people become immune to malaria and why some ethnic groups living in malaria endemic areas are less susceptible than others. The complexity of parasite-host interactions and the genetic diversity of the parasites as well as the human host complicate our strategy to address this issue. In this mini-review we discuss and summarize what we have learned about African ethnic differences in susceptibility to malaria from immuno-epidemiological studies. Additionally, we suggest research topics that might be of great value for dissecting the mechanisms of protection by providing new insights into molecular interactions between the parasite and the host.